Engineering the precursor supply pathway in Streptomyces gilvosporeus for overproduction of natamycin / 生物工程学报

Natamycin is a safe and efficient antimycotics which is widely used in food and medicine industry. The polyene macrolide compound, produced by several bacterial species of the genus Streptomyces, is synthesized by type Ⅰ polyketide synthases using acetyl-CoA, malonyl-CoA, and methylmalonyl-CoA as substrates. In this study, four pathways potentially responsible for the supply of the three precursors were evaluated to identify the effective precursor supply pathway which can support the overproduction of natamycin in Streptomyces gilvosporeus, a natamycin-producing wild-type strain. The results showed that over-expressing acetyl-CoA synthetase and methylmalonyl-CoA mutase increased the yield of natamycin by 44.19% and 20.51%, respectively, compared with the wild type strain under shake flask fermentation. Moreover, the yield of natamycin was increased by 66.29% compared with the wild-type strain by co-overexpression of acetyl-CoA synthetase and methylmalonyl-CoA mutase. The above findings will facilitate natamycin strain improvement as well as development of strains for producing other polyketide compounds.

Isolation and expression of two polyketide synthase genes from Trichoderma harzianum 88 during mycoparasitism

Abstract Metabolites of mycoparasitic fungal species such as Trichoderma harzianum 88 have important biological roles. In this study, two new ketoacyl synthase (KS) fragments were isolated from cultured Trichoderma harzianum 88 mycelia using degenerate primers and analysed using a phylogenetic tree. The gene fragments were determined to be present as single copies in Trichoderma harzianum 88 through southern blot analysis using digoxigenin-labelled KS gene fragments as probes. The complete sequence analysis in formation of pksT-1 (5669 bp) and pksT-2 (7901 bp) suggests that pksT-1 exhibited features of a non-reducing type I fungal PKS, whereas pksT-2 exhibited features of a highly reducing type I fungal PKS. Reverse transcription polymerase chain reaction indicated that the isolated genes are differentially regulated in Trichoderma harzianum 88 during challenge with three fungal plant pathogens, which suggests that they participate in the response of Trichoderma harzianum 88 to fungal plant pathogens. Furthermore, disruption of the pksT-2 encoding ketosynthase–acyltransferase domains through Agrobacterium -mediated gene transformation indicated that pksT-2 is a key factor for conidial pigmentation in Trichoderma harzianum 88.

Predictive criteria of insignificant prostate cancer: what is the correspondence of linear extent to percentage of cancer in a single core?

Objective The aim of active surveillance of early prostate cancer is to individualize therapy by selecting for curative treatment only patients with significant cancer. Epstein’s criteria for prediction of clinically insignificant cancer in surgical specimens are widely used. Epstein’s criterion “no single core with >50% cancer” has no correspondence in linear extent. The aim of this study is to find a possible correspondence. Materials and Methods From a total of 401 consecutive patients submitted to radical prostatectomy, 17 (4.2%) met criteria for insignificant cancer in the surgical specimen. The clinicopathologic findings in the correspondent biopsies were compared with Epstein’s criteria for insignificant cancer. Cancer in a single core was evaluated in percentage as well as linear extent in mm. Results Comparing the clinicopathologic findings with Epstein’s criteria predictive of insignificant cancer, there was 100% concordance for clinical stage T1c, no Gleason pattern 4 or 5, ≤2 cores with cancer, and no single core with >50% cancer. However, only 25% had density ≤0.15. The mean, median and range of the maximum length of cancer in a single core in mm were 1.19, 1, and 0.5-2.5, respectively. Additionally, the mean, median, and range of length of cancer in all cores in mm were 1.47, 1.5, and 0.5-3, respectively. Conclusion To pathologists that use Epstein’s criteria predictive of insignificant cancer and measure linear extent in mm, our study favors that “no single core with >50% cancer” may correspond to >2.5 mm in linear extent. .